var register = window.document.getElementById('register')
let login = window.document.getElementById('air-login');
let air_register = window.document.getElementById('air-register');
let back = window.document.getElementById('back');
register.onclick = function (){
    login.hidden = true;
    air_register.hidden = false;
}
back.onclick = function (){
    login.hidden = false;
    air_register.hidden = true;
}

